Question

An element M has an atomic number 9 and atomic mass 19 . how it's ion will be represented

Answer 1

ion is change atom hence you didn't write that how many electron it will donate or take its ion is M+

Answer 2

Answer: $[F^-]$

Explanation:

Mass number is defined as the sum of number of protons and neutrons that are present in an atom.

Mass number = Number of protons + Number of neutrons = 19

Atomic number is defined as the number of protons or number of electrons that are present in an atom.

Atomic number = Number of electrons = Number of protons = 9

The element which donates the electron is known as electropositive element and forms a positively charged ion called as cation. The element which accepts the electrons is known as electronegative element and forms a negatively charged ion called as anion.

Electronic configuration of atom with 9 electrons i.e. fluorine is:

$[F]=1s^22s^22p^5$

Fluorine atom will gain one electron to gain noble gas configuration and form fluoride ion with -1 charge.

$[F^-]=1s^22s^22p^6$